Over many years, analytical techniques, whether based on genomics, proteomics or immunology, have progressed and have attained remarkable levels of sensitivity. These techniques are based on the recognition of elements of interest or biological targets, which must be extracted from the other elements present in the sample, whether it is obtained in vivo or ex vivo. If the target is absent or is at a level that is too low relative to the sensitivity of the method of analysis, measurement will not be possible.
The methods of sample preparation aim to capture the required targets and bring them in contact, after concentration, with a functionalized surface, on which a measurement is performed. They are very interesting as they make it possible, by concentrating said target, to relax the constraint on the sensitivity of measurement. In contrast, they are ineffective if the target is not present in the sample obtained. This drawback is evident, for example, during blood analysis, where the trend towards reduction of the sample volume has been adversely affected by the presence or absence of the element being sought and by the sensitivity of the measurement system.
A conventional method is the mixing of nanoparticles bearing recognition sites, such as nanobeads, with the sample containing the target and then carrying out recognition in bulk and finally recovering these nanoparticles by centrifugation or magnetic attraction before performing a controlled salting-out of the targets captured on a measurement surface.
Another known method consists of re-circulating the fluid to be tested over a surface that has the recognition sites in question.
The problems in testing body fluids circulating in the human body can be understood similarly. In the example where the volume to be tested is all of the blood or cerebrospinal fluid, by analogy it is possible to envisage the same approach, which consists of injecting metallic and/or magnetic nanoparticles into the body fluid or under the skin, leaving them to recognize the targets and then recovering them for example by application of a local magnetic field or by filtration in an extracorporeal circuit. This approach requires a very thorough investigation of the particles injected with respect to toxicity and filtration in the kidneys, the liver, etc. A problem that has still not been solved is satisfactory recovery of the injected particles.
To counter these problems and notably the risk of triggering immune reactions and toxicity reactions that can arise when said nanoparticles are injected into the human body, the solutions developed to date are generally based on encapsulation of these metallic and/or magnetic nanoparticles in various materials and in particular in biocompatible polymers. Depending on the porosity of said polymer, it can act as a filter, blocking biological species exceeding a certain size. In this context, “biological species” means cells, molecules, viruses, bacteria or antibodies.
In the article “Multi-reservoir device for detecting a soluble cancer biomarker”, K. D. Daniel et al., Lab on a Chip, 2007, Vol. 7, the authors use magnetic iron oxide nanoparticles functionalized with antibodies for binding specifically to targets. To overcome a problem of instability, these nanoparticles are placed in wells of PDMS behind a polycarbonate membrane with pores of 10 nm. The biomarkers can pass through the membrane but the nanoparticles cannot, and therefore remain encapsulated. Detection is performed directly in the device by fluorescence.
Patent document US-A1-2007/0122829 describes a device for measuring the concentration of an analyte in a fluid by means of a detecting agent of the type of a macroporous polymer substrate matrix coupled to a ligand, within an at least partially permeable housing.
For its part, patent document US-A1-2004/0157951 discloses a measuring device comprising, on the one hand, a core for example of the hydrogel type, which can contain an agent capable of binding reversibly to an analyte and, on the other hand, a polymer coating with selective permeability. Detection is performed in situ by measurement of fluorescence.
In these known devices, the use of a coating or of encapsulation improves the performance of the measuring device either with respect to the efficiency of contrast, tolerance to the tissues or the capture capacity.
However, a major drawback of these known devices is that they are not designed for recovering the nanoparticles, such as nanobeads or nanospheres, after they are brought in contact with the required targets in the fluid in question, notably for capturing these targets or for analysis by MRI (magnetic resonance imaging). In other words, the problem of what becomes of the nanoparticles injected in vivo is not really tackled in the prior art.